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In this June 30, 2016, file photo, Defense Secretary Ash Carter speaks during a news conference at the Pentagon.

U.S special operations forces launched a rescue mission to retrieve two men kidnapped by insurgents in Afghanistan last month, but the hostages were not there when the rescue team arrived, U.S. defense officials said Thursday.

Pentagon press secretary Peter Cook said the rescue mission was approved by Defense Secretary Ash Carter and authorized by the president. Cook said no U.S. personnel or civilians were injured and added that he would not provide any more details "in order to protect the safety of hostages and operational security."

According to defense officials, the mission was delayed one day because of questions about the intelligence and whether the hostages, an American and an Australian who worked at the American University of Afghanistan, were there. Officials would not provide the precise timing or location of the rescue attempt because they said it could jeopardize any possible future operations.

Because of questions about the intelligence — including the degree of confidence in the information that the men were at that location — administration officials did not forward the mission request to President Barack Obama until the next day, officials said. Obama approved the mission, and commandos went out that next night.

The officials said that when U.S. commandos arrived at the location, they killed seven enemy fighters. They said that based on interviews with people at the site, it's still not clear if the hostages were ever there.

The officials were not authorized to discuss the matter publicly, so spoke on condition of anonymity.

The two men were kidnapped from their vehicle as they traveled from the university to their residence in Kabul last month. The rescue was attempted not long after their kidnapping.